It is previously known to reform, using a mechanical tool, a blank of plastic material into an intermediate preform or into a container.
Thus, it is known to reform a tubular blank into an intermediate preform by extending the blank in its axial direction which simultaneous orientation of its material. This takes place once the material in the blank has been set at an elevated temperature, whereafter, for example, a rod displaces the bottom of the blank relative to the mouth portion of the blank.
U.S. Pat. No. 4,580,968 describes an alternative technique in which a tubular blank is reformed into an intermediate preform in which the material of the blank passes through a gap in a mechanical forming tool, the gap width being less than the material thickness of the blank. In such instance, a transition zone is moved in the axial direction of the blank between substantially amorphous plastic material (thick material) and oriented material (thin material) under the reduction of the amount of amorphous (thick) material and increase of the amount of oriented (thin) material.
On displacement of the transition zone, the plastic material is oriented. This patent describes an embodiment in which the gap is formed between a draw ring and a mandrel located within the blank. Displacement of the transition zone is realized in that the mandrel displaces a blank placed on the mandrel in relation to the draw ring, amorphous material in the blank passing through the gap and being oriented in the direction of displacement of the transition zone.
The above-described orientation of the plastic material in a blank by means of a mandrel and a draw ring is generally preceded by a setting of the temperature of the material at an elevated level. For example, for polyethylene terephthalate, hereinafter generally abbreviated to PET, a temperature is normally selected which slightly exceeds the glass transition temperature of the material, however, the temperature may also be in the region of or slightly less than the glass transition temperature of the material. Hereinafter, the designation TG will generally be employed to indicate the glass transition temperature of the plastic material. On entry into the above- mentioned gap, the material is generally at the elevated temperature.
The material then passes through the gap, it being required that the contact surface of the material against the draw ring is at a temperature less than a certain maximum temperature. This permitted maximum temperature is determined by the material in the draw ring which forms an abutment surface against the plastic material in its transition zone and by the relevant plastic material. The above condition regarding maximum temperature of the plastic material also applies to the contact region between the plastic material and the mandrel disposed within the blank. A further requirement related to adjustment of the temperature of the plastic material is that such temperature adjustment must, for reasons of process engineering and also for reasons of production capacity, if possible be effected with as slight an influence as possible on the cycle time of the equipment and preferably without affecting this cycle time whatsoever. Naturally, this requirement is conditioned by the desire of maintaining the capital cost per produced unit as low as possible. Moreover, in certain physical applications there are requirements that the temperature of the plastic material display minimal variation from one blank to another. In the above-described orientation of plastic material by means of a gap, it is desirable for certain plastic materials that the material temperature vary by at most approx. 2.degree. C.
EP 204 810 describes a technique in which a hot mandrel is inserted in a preform of thin plastic material and progressively heats the material during simultaneous expansion of the preform as the material of the preform is brought into abutment against and displaced over the outer defining surface of the mandrel. A drawback inherent in this technique is that the temperature of the mandrel must be kept relatively high, which, for certain plastic materials such as PET, leads to undesirably high friction.
In all of the above-described physical applications, the plastic material is, as a rule, given an elevated temperature before the reforming operation, since the elevated temperature is normally a prerequisite to enable application of the technique involved and in order that the product obtain the contemplated properties. The heating is effected in accordance with prior art using radiation energy. Because of the characteristics of the plastic material, such heating has a low level of efficiency. In order to reduce the heating time, use is made, therefore, of high temperatures at the radiation source, which, however, leads to problems if the blank remains in the heating position for too long. Such unintentional extended heating time often occurs in disruptions in the production process, for example an interruption in any of the processing stages which follow after heating of the blank. Such undesirable extension of the heating time in operational disruption will often result in sticking of the blank in the heating position or, at worst, in the blank catching fire unless special measures are implemented to screen off or remove the blank from the radiation source when the unintentional disruption occurs. It is obvious that if a blank sticks in the equipment, a relatively lengthy disruption in production will occur, in particular if the heating devices must be cooled in order to enable removal of the stuck blank. Both such disruptions and extra arrangements included in the equipment to screen off the blank from the radiation source in connection with production disruptions entail extra costs which render production and, thereby, the product itself more expensive.
It will be obvious to one skilled in the art that there are, in many technical contexts, needs for a rapid temperature conditioning of plastic material, often in combination with desires for slight deviation in the temperature of the material for which the temperature conditioning has been carried out. In addition, there are often requirements that the temperature of the material in all parts of the blank be at the predetermined temperature. The term "temperature conditioning" is also here taken to mean cooling of the plastic material.